Why does the oil pressure suddenly drop from 40psi to 10psi. on 2006 Chevrolet Silverado 2500 HD

I have the exact same problem with my 2006 2500HD with 6.0 engine. Driving down the interstate and the oil pressure went from the normal 40psi to around 10 psi on the gauge. Only reason I noticed it is because the rocker arms or lifters started clicking. I took half the damn engine apart to replace the oil pump and still only 10 psi and lifters rattling. Not sure what to do next. Unfortunately the Chilton repair manual for this truck is useless. Incorrect parts shown etc. Also, no drain on the radiator. Whose brainstorm was that at GMC. Any ideas on the what else the problem may be?

Asked by for the 2006 Chevrolet Silverado 2500 HD
try and look under tsb's hope this helps
1 more answer
I juss went through this with mine. A good gm mechanic will know what I'm talking about. I f you take the oil pump pick up tube out there is a o ring in the connection it goes bad and will loose prime after oil warms. This is really easy to over look even if pump has been replaced often old pump is still good. My engine had the same sounds as well. good luck
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